Production of spray metal negatives of models



April 28, 1942.

M. STCSSEL PRODUCTION OF SPRAY METAL NEGATIVES OF MODELS Filed May 29,1940 Patented Apr. 28, 1942 UNITED STATES PATENT OFFICE PRODUCTION OFSPRAY METAL NEGATIVES OF MODELS Max Stiissel, New York, N. Y., assignorto Otto Stossel, Chicago, Ill.

Original application May 22, 1939, Serial No. 274,951. Divided and thisapplication May 29,

The invention relates to the production of spray metal negatives ofmodels, and particularly the production of molds, dies, patterns, or thelike. of the type that are particularly useful in the casting or moldingof plastics such as synthetic resins, rubber, Celluloid, or glass andthe like. This is a division of my application Serial No. 274,951, filedMay 22, 1939.

At the'present, molds for this use are generally produced by cutting themolds from solid metal blocks by means of machining and engraving tools.This method involves considerable time and expense and is notcommercially practicable for low-cost production, except when the moldsthus made are used in. mass production, where the cost of the mold canbe distributed over numerous products made therefrom. Even then thelength of time necessary to produce a mold is a material drawback.

A few attempts have been made to produce molds for this work by sprayingmetal upon a model or a. positive and thus forming a mold or negative.Such attempts were unsuccessful because of distortion and inaccuracy andthe tendency or the sprayed metal to peel oii the model, particularlywhen spraying with metals having a fusion point above 600 C. Thistendency to peel is apparently due to uneven thermal stresses producedin the metal when it is sprayed upon the model and is particularlyprevalent when the metal is sprayed to a thickness exceeding 0.1millimeter, or 0.0025 inch. This peeling makes it impossible in manycases to directly spray an accurate negative or mold having sufficientstrength or rigidity for any practical use.

Further such difllculties are encountered when the model of the articleto be reproduced is formed of some relatively soft material such aswood, plaster-oi-Paris or many of the fibrous materials used to makemodels. In all such instances, therefore, the model does not permit thedirect spraying thereonto of a spray metal of relative hardness, and/orhigh fusion point, to provide a usable negative or mold.

It is the purpose of my present invention to produce an accurate andusable negative or mold economically and commercially by spraying amodel, either the original or a reproduced model, in such a manner as toovercome the heretofore mentioned difficulties, a well as other defectsand limitations.

Further objects and their resultant advantages will be apparent from thefollowing description taken in connection with the following drawing inwhich:

Fig. 1 is a cross-sectional side elevation of a model havingsuperimposed low and higher melting point spray metal layers;

Fig. 2 is a. cross-sectional side elevation of a structure as shown inFi 1 having additionally a wire form embedded in spray metal;

Fig. 3 is a cross-sectional side elevation of the spray metal layersshown in Fig. 1 mounted in a frame and having a superimposed furtherspray metal layer;

Fig. 4 is a cross-sectional side elevation of a spray metal coat formedon a model with the interposition of a thin layer of a low melting pointmetal;

Fig. 5 is a cross-sectional side elevation of a two-part or separablemold; and

Fig. 6 is a cross-sectional side elevation of a structure for applying ametal foil to the surface of a model in accordance with the invention.

In accordance with the invention, a first negative or mold is made of ametal of low melting point, such as tin, zinc or cadmium, by sprayingsuch metals onto the model to be reproduced. The negative or mold madein this manner is then used for the production, by metal spraying,

of a second or duplicate model or positive of a higher melting pointmetal from which a second negative or final mold may be made.

Referring to the drawing the first negative or mold may be made, forinstance, as follows: As illustrated (Fig. 1), a model i, of for examplewood, is to be reproduced. This model i the first or master model andmay be roughened, if desired, by any suitable means, such as sanding orsandblasting. The model is coated with a layer 3a of tin or othersuitable metal of low melting point by spraying the top and sides of themodel as shown in Fig. 1. Additional layers 5a of zinc or similarmaterial are sprayed over the entire coated model so as to completelycover the coated model. The layers 5a of Zinc may be increased to anydesired thickness by repeated sprayings to form a negative or mold ofsatisfactory strength. After the zinc has reached the desired thickness,the negative or mold made up of the layer 3a of tin and layers 5a ofzinc, is separated from the positive or master model i and the flashingor rim I00 may .be removed, if desired, by any suitable method, such aschiseling or milling.

If desired, a strengthening cage or wire form I (Fig. 2), shaped asclosely as possible to the .iorm of the model, may be embedded in thespray model and thereafter spraying additional layers of spray metalover the coated model and form. Because of the added rigidity of thewire 1 the negative or mold is further strengthened.

The negative or first mold produced by either of the foregoingmethods, 1. e., with or without the reinforcing wire form 1, is thenused in the following manner for the production of a second model, itbeing understood, of course, as previously stated,'that the first ormaster model was of such material that it could not be sprayed with ahard metal or a metal of high melting point in the first instance.

It is preferred to place the first mold in a frame support 8 (Fig. 3) inorder to insure against possible deformation or distortion of the firstmold which is of relatively soft metal, during the production of asecond model, or the reproduction of the master model. The frame support6 (Fig. 3) has its upper edge channeled at H to receive the edge portionof the mold an upper clamping plate or frame l2, preferably ofsufficient width to overlap the top surface of the mold, may be securedto the frame support by screws l3 or by any other suitable means. Theinner edge of the plate or frame 12 may be beveled as at H and ispreferably roughened in any suitable manner.

It is preferred to further support the mold 5 by filling the framesupport 6 beneath the mold 5 with some supporting material such as metalor sand I6 and to close the frame support with a bottom plate ll. Inthis manner the first negative or mold is securely and rigidly supportedagainst any possible distortion or deformation during the production ofthe second positive or model or the reproduction of articles like themaster model. I

The layer 3a of tin or other low melting point metal remains on theinner surface of the first negative or mold 5 after its removal from themodel, thus presenting a suitable surface for the next succeedingapplication of spray metal.

. It is desirable to coat the beveled edge I14 of the plate or frame l2(Fig. 3) with tin to facilitate separation of the second positive fromthe first mold. This maybe done by spraying, dipping or plating. Theinner surface of the first negative or mold 5 is then sprayed withsuccessive layers of a harder metal of higher melting point, such asbronze, than the metal of the mold, until a second positive or model ofthe desired thickness of the metal 20 has been formed. It is ofadvantage to apply these latter layers of metal 20 by first spraying athin layer over the entire inner surface of the mold and against theinner sloping edge H of the plate or frame l2, after which the metal 20is. preferably thickened around the marginal edge and against the edgeH. In this way, the final layers are retained and held in contact withthe mold, i. e., the metal is prevented from peeling or separating fromthe surface of the first mold 5. As previously stated, additional layersof the harder metal may be sprayed on until any desired thickness hasbeen reached, preferably until the center is as thick as the edge.Ordinarily, a thickness of 0.25 to 0:4 inch is sufficient to give thedesired and necessary strength to the second positive or model.

After a second positive or model of the desired thickness or strength ofmetal 20 has been prepared, it may be removed from the first mold byheating them to the melting point of the low melting point metal. In thespecific embodiment illustrated in the drawing, the layer 3a of tin isso heated, thus severing the bond between the second positive or model,composed of the relatively harder metal 20, and the first negative ormold 5, permitting the two to be readily separated. After separation,the second positive or model 20 is preferably carefully cleaned bybrushing while still hot, dipping into an acid or by any other suitablemethod.

This second model of the metal 20 can then be used for making a secondmold of a metal of greater hardness and higher melting point than couldbe obtained directly from the original model. The second mold may bemade, for instance, in the following manner:

The second model of spray metal-20 is, for example, clamped in andsupported by a steel frame support 6 (Fig. 4), as described inconnection with the first negative 5 (Fig. 3) in order to avoid possibledistortion of the model while the metal of the mold is being sprayedthereon. For example, the model 20 may be inverted and seated in therecessed frame support 6, as shown in Fig. 4, and held therein by anupper clamping plate or frame Ila similar to frame l2, having preferablya sloping edge Ila and an inner diameter smaller than that of plate orframe I 2 and preferably of proper size to retain the model 20 withinthe frame support 6. As in the case of preparing the second model, thelower side of the model, when placed in the frame support 6, ispreferably also supported by a metal It or sand, or some other suitablematerial.

The model 20 is covered with a thin coating 24 (Fig. 4) of metal ofrelatively low melting point such as tin, cadmium or zinc. This coatingmay be applied by hot dipping or, preferably, by electro-plating and notonly aids in the adherence of the metal of the negative or mold to themetal of the model but also facilitates separation of the two after thenegative or mold is completed.

Assuming the model has been prepared by electro-plating a coating 24 oflow melting point metal thereon, it is then sprayed with successivelayers 26 of suitable higher melting point metal until a spray metalcoating of the desired thickness has been produced[ While spraying thecoated model, the same being preferably clamped in a suitable frame, thelayers 26 of sprayed metal will build up under the inclined edge Ha ofthe plate or frame I211. The spray metal negative 26 is finallyseparated from the model 20 by melting the coating 'Mof low meltingpoint metal.

The model may be notched or grooved, if desired, as at 25, which notchesor grooves are filled with low melting point metal. This additionalamount of low melting point metal becomes fused and seeps in between themodel and the negative or mold when they are heated and furtherfacilitates separation.

In certain cases where extreme precaution is required to preventdistortion of the model or matrix while the metal of the negative ormold is being sprayed thereon, it may be desirable to cool the modelwhile the metal of the negative or mold is so sprayed. This can beaccomplished very readily by circulating a cooling medium through thelower portion of the frame support 6.

In certain classes of molding, both surfaces of the molded article mustbe finished. In such cases, a two-part mold must be employed. In Fig.there is illustrated a two-part mold of this character, both parts ofthe mold being made in accordance with the processes outlined above.Such a mold is particularly adaptable to the manufacture of articles ofsynthetic resins and may comprise two parts 3| and 32, both made by thespraying of high melting point metals upon a model, as previouslyoutlined. Each of the portions of the mold is preferably supported inframes 33 and 34, respectively, which are backed with suitable materialto give the necessary rigidity to the two sections of the mold. The twoportions of the mold are provided with studs 31 and guides 38,respectively, to cause proper approach of the two sections of the moldwhen they are brought together. Where, as will appear from the specificembodiment illustrated in the drawing (Fig. 5), the surfaces of the.mold portions 3| and 32 constitute substantial negatives of each other,they represent thus, one a negative and the other a duplicate of one andthe same model surface.

When the original model, due to the material of which it is made, willnot permit the direct spraying of metal thereon, inter alia, because ofthe fact that sprayed particles of metal embed in the surface of themodel, resulting in either a misshapen mold or in a mold having anundesirable finish, it is of advantage to first cover such model with asheet of relatively thin metal foil such as tin foil and thereafterspray the foil coated model. Such foil, as for instance foil 46 (Fig.6), may be pressed, such as by hand, into as close contact as possiblewith the model I, after which the model thus coated may be placed in thelower portion 41 of a frame. Preferably, the tin foil is held on themodel by a plaster collar, or the like ll, which extends around andbeneath the model.

The tin foil is then forced into extremely close contact with the uppersurface of the model such as by a flexible rubber diaphragm 48 held inthe upper portion 50 of the frame which may be clamped to the lowerportion by clamps 5|. The rubber diaphragm is forced into tight contactagainst the upper portion of the mold by means of a fluid admitted underpressure between the upper side of the rubber diaphragm and, the top ofthe upper frame portion 30 through an orifice l2 and a conduit 33. Ithas been found satisfactory to use pressures of the magnitude of aboutfifty pounds per square inch to get the desired contact of themetal foilwith the upper surface of the mold. After the model has thus beenprepared, it may be used for the production of a mold bymetal spraying.

It will be obvious to those skilled in the art that molds may beproduced in accordance with the foregoing much quicker than the-usualweeks of time now required and at a cost materially less thanheretofore. Accurate molds may be produced at a very low cost, whichmolds are wholly satisfactory and adequate for the reproduction ofmolded articles, even if such articles are desired for samples or smallconsumption rather than for mass production, in which case it washeretofore economically impossible to do this because of the expense inproducing a mold.

The material of which a sprayed mold is to be made may be selectedaccording to the conditions to which it is to be subjected or the use towhich it is to be put. For example, aluminum or aluminum alloys, bronzeor similar metals may be used if little strain is to be put on the moldor if the number of articles to be made therefrom is small. If, on theother hand, however, the mold is to be used for mass production, or iffor any other reason it must be of harder material, such metals assteel,,' nickel, or chromenickel alloys. or the like may be used.

It will be apparent to thoseskilled in the art that minor variations anddeviations from the foregoing processes as described may be indulged inwithout departing from the spirit and scope of this invention, asdefined in the appended claims.

I claim:

1. Method of making a spray metal negative of relatively hard metal froma model the surface of which is non-metallic and does not permit thedirect spraying with such metal, which comprises the steps of spraying acoating of metalof relatively low melting point on such model, saidcoating beingstrippably bonded to said model, separating said model fromthe spray metal negative thus formed, spraying a coating of metal ofrelatively higher melting point on said negative to form a spray metalduplicate of said model, separating said duplicate from said negative,

, spraying said duplicate with a relatively hard metal to form a secondnegative and separating said duplicate from said second negative.

2. Method of making a spray metal negative of relatively hard metal froma model the surface of which is non-metallic and does not permit thedirect spraying with such metal, which comprises the steps of spraying acoating of metal of relatively low melting point on such model, saidcoating being strippably bonded to said model, separating said modelfrom the spray metal negative thus formed, spraying a coating of metalof relatively higher melting point on said negative to form a spraymetal duplicate of said model, heating said negative at least on itscontacting surface with said duplicate to the melting point of said lowmelting point metal, recovering said duplicate, spraying said duplicatewith a hard metal to form a second negative and separating saidduplicate from said second negative.

3. Method in accordance with claim 2 in which said low melting pointmetal is at least one member selected from the group consisting of tin,zinc and cadmium;

4. In the method of making a spray metal negative of relatively hardmetal from a model the surface of which is non-metallic and does notpermit the direct spraying with such metal, the steps comprisingspraying a coating of metal of relatively low. melting point on suchmodel, said coating being strippably bonded to said model, separatingsaid model from the spray metal negative thus formed, spraying a coatingof metalof relatively higher melting point on said negative to form aspray metal duplicate of said model and separating said duplicate andsaid negative by melting of! the latter.

5. The steps in accordance with claim 4 in which said low melting pointmetal is at least one member selected from the group consisting of tin,zinc and cadmium.

6. Method ofmaking a spray metal negative of relatively hard metal froma model the surface of d 'tively higher melting point on said niitive toform a spray metal duplicate or said model, heating said negative atleast on its contacting surface with said duplicate to the melting pointof said low melting point metal, recovering said duplicate, applyinz arelatively thin coating 01' a low melting point metal to said duplicate,spraying said coated duplicate with a relatively hard metal of a highermelting point than said l st mentioned coating metal to form a secondnegative and separating said duplicate from said second negative bymelting said thin coating of low melting point metal.

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